1. Field of the Invention
The present invention relates to a thermosetting resin composition, and a prepreg and a laminated sheet for electrically insulating material using the thermosetting resin composition.
2. Prior Art
As printed wiring boards for electronic appliance, laminated sheets mainly using an epoxy resin have been widely used. However, in accordance with tendencies that a pattern becomes finer due to the increase in the mounting density in electronic appliance, the surface mount system is generally employed, the signal propagation velocity becomes higher, and the frequency of the signal used becomes higher, a development of printed wiring board materials having a low dielectric loss and an improved heat resistance are strongly desired.
As a prior art of a resin composition or laminated sheet using an epoxy resin as a curing agent and using a copolymer resin comprising styrene and maleic anhydride, for example, Japanese Unexamined Patent Publication No. 109476/1974 has a description about a flexible printed wiring board from a flexible epoxy resin and a copolymer resin which comprises styrene and maleic anhydride, wherein a reactive epoxy diluent and an acrylonitrile-butadiene copolymer are necessary for imparting flexibility to the printed wiring board. In addition, Japanese Unexamined Patent Publication No. 221413/1989 has descriptions about a copolymer resin having an acid value of 280 or more, which is obtained from an epoxy resin, an aromatic vinyl compound, and maleic anhydride, and about an epoxy resin compound containing dicyanamide. Further, Japanese Unexamined Patent Publication No. 25349/1997 has descriptions about a prepreg and a laminated sheet material for electrical appliance, comprising a brominated epoxy resin, a copolymer resin comprising styrene and maleic anhydride (epoxy resin curing agent), a styrene compound, and a solvent. Japanese Unexamined Patent Publications No. 17685/1998 and No. 17686/1998 have descriptions about a prepreg and a laminated sheet material for electrical appliance, comprising an epoxy resin, a copolymer resin of an aromatic vinyl compound and maleic anhydride, and a phenolic compound. Japanese Unexamined national Patent Publication (kohyo) No. 505376/1998 has descriptions about a resin composition, a laminated sheet, and a printed wiring board, comprising an epoxy resin, a cross-linking agent for carboxylic anhydride-type epoxy resin, and an allyl network-forming compound. However, these prior art materials do not have performance required for the tendency that the pattern becomes finer and the frequency of the signal becomes higher, that is, they do not have low dielectric loss, excellent heat resistance, excellent moisture resistance, and excellent adhesion to a copper foil.